The proposed research has two major objectives: (1) To determine if the tumorigenic potential of chemically transformed rat esophageal epithelial cells is associated with: (a) alterations in the content and distribution of cellular microfilaments and/or microtubules; (b) expression of p21 proteins encoded by the retroviruses, c-Harvey-ras and c-Kirsten-ras, (c) the ability of the cells to invade esophageal tissues in vitro; (d) the contents of cell surface laminin and fibronectin; and, (e) the activities of IV collagenase and plasminogen activator; and, (2) To initiate the development of a quantitative assay for the neoplastic transformation of rat esophageal epithelial cells with chemical carcinogens. Immunological methods will be used to determine the distribution and content of actin and tubulin and the content of cell surface laminin and fibronectin in non-tumorigenic, pre-neoplastic and squamous cell carcinoma-producing esophageal epithelial cell lines. The ability of these cell lines to invade esophageal tissues in vitro will be assessed using a modified amnion chemotaxis chamber. Type IV collagenase activity in the cells and in the culture media will be determined by measuring the release of soluble radiolabelled peptides from radioactive type IV collagen. Plasminogen activator activity in cells and in media will be determined by measuring the release of soluble 3H-fibrinopeptides from 3H-fibrin-coated plates. To quantitate the frequency of esophageal epithelial cell transformation, cultures will be treated with N-methyl-N-nitro-N-nitrosoguanidine under conditions that are permissive for their growth and, after a period of time, shifted to conditions that select for foci of carcinogen-altered cells. Cultures derived from these foci will be monitored for tumorigenic potential in syngeneic rats. It is anticipated that the proposed studies will lead to the identification of factors that are associated with the tumorigenic potential of esophageal epithelial cells. Information regarding these factors could lead to the development of strategies to inhibit tumor growth. In addition, the quantitative assay could provide a more rapid method for identifying carcinogens for the esophagus and for determining their relative potency.